DE19932060A1 - Process for the production of C¶5¶ / C¶6¶ olefins - Google Patents

Abstract

The process for the preparation of C 5 - / C 6 -olefins from an output stream containing olefinic C 4 -hydrocarbons is characterized in that DOLLAR A a) in the presence of a metathesis catalyst which comprises at least one compound of a metal of VI.b, VII.b or VIII. subgroup of the periodic table of the elements, a metathesis reaction is carried out, in the course of which 1-butene, 2-butene and isobutene contained in the starting stream are converted to a mixture of C 2 -C 6 -olefins and butanes, DOLLAR A b) the discharge stream thus obtained is first separated by distillation into a low boiler fraction A consisting of C 2 -C 4 -olefins and butanes or of C 2 -C 3 -olefins, which is discharged, and into one of C 4 -C 6 -olefins and butanes existing high boiler fraction, DOLLAR A c) the high boiler fraction obtained from b) then by distillation into a low boiler fraction B consisting of butenes and butanes, one of pentene and methyl butene existing middle boiler fraction C and into a high boiler fraction D consisting of hexene and methyl pentene, DOLLAR A d) wherein the fractions B and / or C are completely or partially returned to process step a) and fraction D is discharged as a product.

Description

The present invention relates to a process for converting olefinic C ₄ hydrocarbons, for example from steam crackers or FCC crackers, into pentenes and hexenes by means of a metathesis reaction. Propene is obtained as the desired process co-product.

In its simplest form, olefin metathesis (disproportionation) describes the reversible, metal-catalyzed transalkylidation of olefins by breaking or reforming C = C double bonds according to the following equation:

A distinction is made in the special case of metathesis of acyclic olefins between self-metathesis, in which an olefin is mixed into a mixture of two olefins different molar mass (for example: propene → ethene + 2- Butene), and cross or co-metathesis, which is a reaction of two describes different olefins (propene + 1-butene → ethene + 2-pentene). Is one of the reactants ethene, one generally speaks of one Ethenolysis.  

In principle, homogeneous and heterogeneous are suitable as metathesis catalysts Transition metal compounds, especially those of VI. to subgroup VIII of the periodic table of the elements as well as homogeneous and heterogeneous Catalyst systems in which these compounds are contained.

Different metathesis processes that originate from C ₄ streams have been described.

US 5,057,638 relates to a process for the preparation of 1-hexene, comprising the process steps:

• a) metathesis of 1-butene to a mixture of 3-hexene and ethene,
• b) separating the 3-hexene from the product mixture obtained in step a)
• c) reaction of the 3-hexene with a reactive hydrogen, preferably from Water or carboxylic acid derived, containing electrophile under acid Conditions which include the addition of the electrophilic components and the Allow C = C bond (e.g. hydration),
• d) cracking the product from step c), e.g. B. by dehydration Preparation of a mixture of n-hexenes, which 1-hexene in contains economically acceptable amounts.

US 69-821945 (05.05.1969) describes the conversion of short-chain C ₄ -C ₁₂ olefins (preferably α-olefins) into higher olefins by metathesis. The process is characterized in that the starting olefin is brought into contact with a catalyst which contains aluminum, molybdenum or rhenium and silver or copper at 100 to 240 ° C, low-boiling by-products, such as. B. ethene, can be removed from the equilibrium in situ.

The present invention further relates to a combined process for the production of C ₅ / C ₆ olefins with propene as a secondary yield starting from C ₄ cuts from steam or FCC crackers.

Steam crackers are the main source of petrochemical basic chemicals such as ethene, propene, C ₄ olefins and higher hydrocarbons. In the cracking process, it is necessary to transfer large amounts of energy at high temperatures in a time period which is sufficient on the one hand to carry out the cleavage but on the other hand a further reaction of the fission products does not allow. When hydrocarbons are split, the yield of ethene and propene is therefore essentially determined by the

• - Type of hydrocarbons used (naphtha, ethane, LPG, gas oil, etc.)
• - gap temperature,
• - dwell time
• - and the partial pressures of the respective hydrocarbons

certainly.

The highest yield of ethene and propene is achieved at gap temperatures between 800 and 850 ° C and residence times of 0.2 to 0.5 s. The main product in this area is always ethene, whereby the C ₃ / C ₂ discharge ratio of approx. 0.5 to 0.7 can be increased to a small extent by varying the cracking conditions. Worldwide, the need for propene is growing faster than that of ethene. One of the consequences of this is that processes for the downstream utilization of the higher hydrocarbons formed in the cracking process, such as, for. B. C ₄ , gaining in importance with regard to the optimization of the propene yield.

As part of work to improve the value added of steam cracker by-products, the task was to develop a flexibly controllable catalytic process for the production of pure C ₅ - / C ₆ -olefin streams from inexpensively available olefin-containing C ₄ -hydrocarbon mixtures without ethene metering.

The object is achieved according to the invention by a process for the preparation of C ₅ - / C ₆ -olefins from an output stream containing olefinic C ₄ -hydrocarbons, wherein

• a) in the presence of a metathesis catalyst which contains at least one compound of a metal of VIb, VIIb or VIII. Subgroup of the Periodic Table of the Elements, a metathesis reaction is carried out, within the scope of which 1-butene, 2-butene and isobutene contained in the output stream are converted into a mixture C ₂ -C ₆ olefins and butanes are reacted,
• b) the discharge stream thus obtained is first separated by distillation into a low boiler fraction A consisting of C ₂ -C ₄ olefins and butanes, which is discharged, and into a high boiler fraction consisting of C ₄ -C ₆ olefins and butanes,
• c) the high boiler fraction obtained from b) is then distilled into a low boiler fraction B consisting of butenes and butanes, one of Penten and methylbutene consisting of medium boiler fraction C and in one Hexene and methylpentene existing high boiler fraction D separated becomes,
• d) wherein the fractions B and / or C completely or partially in the Process step a) are recycled and fraction D as a product is removed.

The expression "consisting of" does not exclude the presence of smaller ones Amounts of other hydrocarbons.  

In a one-step reaction according to the following equation, a fraction consisting of C ₄ -olefins, preferably n-butenes, isobutene and butanes, is converted over a homogeneous or preferably heterogeneous metathesis catalyst to a product mixture of (inert) butanes, unreacted 1-butene, in a metathesis reaction, 2-butene and optionally isobutene and the metathesis products ethene, propene, 2-pentene, optionally 2-methyl-2-butene, 3-hexene and optionally 2-methyl-2-pentene:

The amount of the branched C ₅ and C ₆ hydrocarbons in the metathesis discharge depends on the isobutene content in the C ₄ feed and is preferably kept as low as possible (<3%).

In order to explain the process according to the invention in more detail, the above equilibrium reaction (without taking isobutene into account) divided three important individual reactions:

1. Cross metathesis of 1-butene with 2-butene

2. Self-metathesis of 1-butene

3. Ethenolysis of 2-butene

Depending on the respective need for the target products propene, 2-pentene and 3-hexene (the term 2-pentene may include, among other things formed isomers, such as cis / trans or 2-methyl-2-butene, the same applies to 3- Hexen) can target the external mass balance of the procedure by shifting it of the equilibrium can be influenced by recycling certain partial flows. For example, the 3-hexene yield is increased if by recycling of 2-pentene in the metathesis step the cross-metathesis of 1-butene with 2- Butene is suppressed, so that no or as little 1-butene as possible is consumed. In the then preferred self-metathesis of 1- Butene to 3-hexene is additionally formed ethene, which in a subsequent reaction reacts with 2-butene to produce the valuable product propene.

Olefin mixtures containing 1-butene, 2-butene and isobutene are obtained as a C ₄ fraction in various cracking processes such as steam cracking or FCC cracking. Alternatively, butene mixtures, such as those obtained in the dehydrogenation of butanes or by dimerization of ethene, can be used. Butanes contained in the C ₄ fraction are inert. Before the metathesis step according to the invention, dienes, alkynes or enynes are removed using customary methods such as extraction or selective hydrogenation.

The butene content of the C ₄ fraction used in the process is 1 to 100% by weight, preferably 60 to 90% by weight. The butene content relates to 1-butene, 2-butene and isobutene.

A C ₄ fraction is preferably used, such as is obtained in steam or FCC cracking or in the dehydrogenation of butane.

Raffinate I or II can be used as the C ₄ fraction, the C ₄ stream being freed from disturbing impurities prior to the metathesis reaction by appropriate treatment on protective adsorber beds, preferably on high-surface area aluminum oxides or molecular sieves.

The low boiler fraction A obtained, in particular the C _2/3 fraction, can be further processed directly as such, fed to the processing sequence of a steam or FCC cracker in order to obtain pure ethene and propene, or can be returned in whole or in part to the metathesis step to increase the yield of pentene / hexene; or used separately to obtain ethene and propene as a pure component (especially as a C _2/3 fraction).

The metathesis reaction is preferably carried out in the presence of heterogeneous, not or only slightly isomerization-active metathesis catalysts carried out from the class of applied to inorganic carriers Transition metal compounds of metals of group VI.b, VII.b or VIII of the periodic table of the elements are selected.

Rhenium oxide on a support, preferably on γ-aluminum oxide or on Al ₂ O ₃ / B ₂ O ₃ / SiO ₂ mixed supports, is preferably used as the metathesis catalyst.

In particular, the catalyst used is Re ₂ O ₇ / γ-Al ₂ O ₃ with a rhenium oxide content of 1 to 20%, preferably 3 to 15%, particularly preferably 6 to 12% (% by weight).

The metathesis is preferably carried out at a temperature of 0 to 150 ° C, particularly preferably 20 to 80 ° C and a pressure of 2 to 200 bar, particularly preferably 5 to 30 bar.  

If the metathesis is carried out in the gas phase, the temperature is preferably 20 to 300 ° C, particularly preferably 50 to 200 ° C. The pressure is in this case preferably 1 to 20 bar, particularly preferably 1 to 5 bar.

As part of work to improve the value creation of steam cracker by-products, the task was also to develop a flexibly controllable process sequence for the utilization of C ₄ cuts. The aim was to convert C ₄ olefins with high added value into higher-priced olefin fractions. Raw C ₄ cuts from steam crackers or FCC crackers are available as feedstock.

The object is achieved according to the invention by a process for the preparation of C ₅ / C ₆ olefins and propene from steam cracker or refinery C ₄ streams, comprising the substeps

• 1. Separation of butadiene and acetylenic compounds by optionally extracting butadiene with a butadiene-selective solvent and subsequent / or selective hydrogenation of butadienes and acetylenic impurities contained in crude C ₄ cut in order to obtain a reaction product, the n-butenes and isobutene and contains essentially no butadienes and acetylenic compounds,
• 2. Separation of isobutene by reaction of the reaction product obtained in the above step with an alcohol in the presence of an acid catalyst to give an ether, separation of the ether and alcohol, which can be carried out simultaneously or after etherification, in order to obtain a reaction product which n -Butene and optionally oxygenate impurities, whereby formed ether can be discharged or split back to obtain pure isobutene and the etherification step can be followed by a distillation step to separate isobutene, with C ₃ -, iC ₄ - and C ₅ -hydrocarbons also possibly being introduced by distillation can be separated in the course of working up the ether, or oligomerization or polymerization of isobutene from the reaction product obtained in the above step in the presence of an acid catalyst, the acid strength of which is suitable for the selective removal of isobutene as oligo- or polyisobutene to obtain a stream which has 0 to 15% residual isobutene,
• 3. Separate the oxygenate contaminants from the discharge of the above Steps on appropriately selected adsorber materials,
• 4. Metathesis reaction of the raffinate II stream thus obtained as described.

The partial step selective hydrogenation of butadiene and acetylenic impurities contained in crude C _{4 cut} is preferably carried out in two stages by contacting the raw C _{4 cut} in the liquid phase with a catalyst comprising at least one metal selected from the group consisting of nickel, palladium and platinum , on a support, preferably palladium on alumina, at a temperature of 20 to 200 ° C, a pressure of 1 to 50 bar, a volume velocity of 0.5 to 30 m ^{3 of} fresh feed per m ^{3 of} catalyst per hour and a ratio of Recycle to feed from 0 to 30 with a molar ratio of hydrogen to diolefins from 0.5 to 50 to obtain a reaction product in which, in addition to isobutene, the n-butenes 1-butene and 2-butene in a molar ratio of 2: 1 to 1:10, preferably from 2: 1 to 1: 2, and essentially no diolefins and acetylenic compounds are present.

The butadiene extraction step from crude C _{4 cut} is preferably carried out with a butadiene-selective solvent, selected from the class of polar aprotic solvents, such as acetone, furfural, acetonitrile, dimethylacetamide, dimethylformamide and N-methylpyrrolidone, in order to discharge a reaction obtained in which the n-butenes 1-butene and 2-butene are present in a molar ratio of 2: 1 to 1:10, preferably from 2: 1 to 1: 2.

The sub-step isobutene etherification is preferably carried out in a three-stage Reactor cascade with methanol or isobutanol, preferably isobutanol in In the presence of an acidic ion exchanger carried out in the flooded Fixed bed catalysts are flowed through from top to bottom, the Reactor inlet temperature 0 to 60 ° C, preferably 10 to 50 ° C, the Initial temperature 25 to 85 ° C, preferably 35 to 75 ° C, the pressure 2 to 50 bar, preferably 3 to 20 bar and the ratio of isobutanol to isobutene 0.8 to 2.0, preferably 1.0 to 1.5, and the total conversion is Equilibrium turnover corresponds.

The substep isobutene separation is preferably carried out by oligomerization or polymerization of isobutene, starting from the reaction discharge obtained after the butadiene extraction and / or selective hydrogenation steps described above, in the presence of a catalyst which is selected from the class of homogeneous and heterogeneous Broensted acids, preferably from heterogeneous contacts which contain an oxide of a metal from subgroup VI.b of the Periodic Table of the Elements, even in the case of an acidic inorganic support, particularly preferably WO ₃ TiO ₂ , in order to generate a current which has less than 15% residual isobutene.

Selective hydrogenation of crude C ₄ cuts

Alkynes, alkynes and alkadienes are due to their tendency to polymerize or their pronounced tendency to form complexes on transition metals in many technical syntheses undesirable substances. They affect the Catalysts used very heavily in these reactions.

The C ₄ stream of a steam cracker contains a high proportion of polyunsaturated compounds such as 1,3-butadiene, 1-butyne (ethyl acetylene) and butenine (vinyl acetylene). Depending on the downstream processing, the polyunsaturated compounds are either extracted (butadiene extraction) or selectively hydrogenated. In the former case, the residual content of polyunsaturated compounds is typically 0.05 to 0.3% by weight, in the latter case typically 0.1 to 4.0% by weight. Since the remaining amounts of polyunsaturated compounds also interfere with further processing, further enrichment by selective hydrogenation to values <10 ppm is required. In order to obtain the highest possible product value of butenes, the overhydrogenation to butanes must be kept as low as possible.

Suitable hydrogenation catalysts are described:

J.P. Boitiaux, J. Cosyns, M. Derrien and G. Lèger, Hydrocarbon Processing, March 1985, p.51-59

Description of bimetallic catalysts for selective hydrogenation of C ₂ -, C ₃ -, C ₄ -, C ₅ - and C ₅₊ -hydrocarbon streams. In particular, bimetallic catalysts made from Gp.VIII and Gp.IB metals show improvements in selectivity compared to pure Pd supported catalysts.

DE-A-20 59 978

Selective hydrogenation of unsaturated hydrocarbons in the liquid phase on a Pd / alumina catalyst. The catalyst is characterized in that the alumina carrier with BET 120 m ² / g is first subjected to a steam treatment at 110-300 ° C and then calcined at 500-1200 ° C. Finally, the Pd compound is applied and calcined at 300-600 ° C.

EP-A-0 564 328 and EP-A-0 564 329

Catalyst which u. a. consists of Pd and In or Ga on carrier. The Catalyst combination enables use without high CO addition Activity and selectivity.  

EP-A-0 089 252

Pd, Au supported catalysts.

The catalyst preparation comprises the following steps:

• - Impregnation of a mineral carrier with a Pd compound calcination under gas containing O ₂
• - Treatment with a reducing agent
• - Impregnation with a halogenated Au compound
• - Treatment with a reducing agent
• - Washing out of the halogen by basic connection
• - Calcination under gas containing O ₂ .

US 5,475,173

Catalyst consisting of Pd and Ag and alkali fluoride on inorganic Carrier.

Advantages of the catalyst: increased butadiene conversion and addition of KF better selectivity to butenes (i.e. less overhydrogenation to n-butane).

EP-A-0 653 243

The catalyst is characterized in that the active component predominantly located in the meso and macropores. The catalyst continues to be characterized by a large pore volume and low Vibrating weight. For example, the catalyst from Example 1 has a vibrating weight of 383 g / l and a pore volume of 1.17 ml / g.

EP-A-0 211 381

Catalyst made of Gp.VIII metal (preferably Pt) and at least one metal made of Pb, Sn or Zn on an inorganic support. The preferred catalyst consists of Pt / ZnAl ₂ O ₄ . The selectivity of the Pt contact is improved by the promoters Pb, Sn and Zn mentioned.

EP-A-0 722 776

Catalyst made of Pd and at least one alkali fluoride and optionally Ag on an inorganic support (Al ₂ O ₃ , TiO ₂ and / or ZrO ₂ ). The catalyst combination enables selective hydrogenation in the presence of sulfur compounds.

EP-A-0 576 828

Catalyst based on noble metal and / or noble metal oxide on Al ₂ O ₃ support with a defined X-ray diffraction pattern. The carrier consists of n-Al ₂ O ₃ and / or γ-Al ₂ O ₃ . Due to the special support, the catalyst has a high initial selectivity and can therefore be used immediately for the selective hydrogenation of unsaturated compounds.

JP 01110594 Pd supported catalyst

Another electron donor is also used. This exists either from a metal deposited on the catalyst, such as for example Na, K, Ag, Cu, Ga, In, Cr, Mo or La, or an additive to Hydrocarbon feed, such as alcohol, ether or N- containing connections. Through the measures mentioned, a Reduction of 1-butene isomerization can be achieved.

DE-A-31 19 850

Catalyst made of an SiO ₂ or Al ₂ O _{3 support} with 10 to 200 m ² / g or ≦ 100 m ² / g with Pd and Ag as active component. The catalyst is primarily used for the hydrogenation of low-butadiene hydrocarbon streams.

EP-A-0 780 155

Catalyst made of Pd and a Gp. IB metal on an Al ₂ O _{3 support} , with at least 80% of the Pd and 80% of the Gp. IB metal in an outer shell between r1 (= radius of the pellet) and 0.8 -r _{1 are} applied.

Alternatively: extraction of butadiene from crude C _{4 cut}

The preferred method for butadiene isolation is based on the physical principle of extractive distillation. By adding selective organic solvents, the volatility of special components of a mixture, in this case butadiene, is reduced. These therefore remain in the bottom of the distillation column with the solvent, while the accompanying substances, which could not previously be removed by distillation, can be removed overhead. The main solvents used for extractive distillation are acetone, furfural, acetonitrile, dimethylacetamide, dimethylformamide (DMF) and N-methylpyrrolidone (NMP). Extractive distillation is particularly suitable for butadiene-rich C ₄ cracking cuts with a relatively high proportion of alkynes, including methyl, ethyl and vinyl acetylene and methyl alleles.

The simplified principle of a solvent extraction from crude C _{4 section} can be represented as follows: The completely evaporated C _{4 section} is fed to an extraction column at the lower end. The solvent (DMF, NMP) flows towards the gas mixture from above and is loaded with more soluble butadiene and small amounts of butenes on the way down. Part of the pure butadiene obtained is fed in at the lower end of the extraction column in order to largely drive off the butenes. The butenes leave the column at the head. In a further column called outgas, the butadiene is freed from the solvent by boiling and then pure distilled.

Usually the reaction discharge of a butadiene extractive distillation is in the second stage of a selective hydrogenation to the butadiene Reduce residual content to values of <10 ppm.  

The C ₄ stream remaining after separation of butadiene is referred to as C ₄ raffinate or raffinate I and mainly contains the components isobutene, 1-butene, 2-butenes and n- and isobutenes.

Separation of isobutene from raffinate I

In the further separation of the C ₄ stream, isobutene is preferably isolated subsequently, since it differs from the other C ₄ components by its branching and its higher reactivity. In addition to the possibility of shape-selective molecular sieve separation, with which isobutene can be obtained with a purity of 99% and n-butenes and butane adsorbed on the molecular sieve pores can be desorbed again using a higher-boiling hydrocarbon, this is done primarily by distillation using a so-called deisobutenizer , with which isobutene is separated off together with 1-butene and isobutene overhead and 2-butenes and n-butane including residual amounts of iso- and 1-butene remain in the sump, or extractive by reacting isobutene with alcohols on acidic ion exchangers. For this purpose, preferably methanol (→ MTBE) or isobutanol (IBTBE) are used.

MTBE is produced from methanol and isobutene at 30 to 100 ° C and slightly overpressure in the liquid phase on acidic ion exchangers. One works either in two reactors or in a two-stage shaft reactor in order to achieve an almost complete isobutene conversion (<99%). The pressure-dependent azeotrope formation between methanol and MTBE requires a multi-stage pressure distillation in order to reproduce MTBE or is achieved by newer technology through methanol adsorption on adsorber resins. All other components of the C ₄ fraction remain unchanged. Since small proportions of diolefins and acetylenes can shorten the life of the ion exchanger by polymer formation, bifunctional PD-containing ion exchangers are preferably used, in which only diolefins and acetylenes are hydrogenated in the presence of small amounts of hydrogen. The etherification of the isobutene remains unaffected.

MTBE is primarily used to increase the octane number of gasoline. MTBE and Alternatively, IBTBE can be used on acidic oxides in the gas phase at 150 to 300 ° C Pure extraction of isobutene can be split back.

Another possibility for separating isobutene from raffinate I is in the direct synthesis of oligo / polyisobutene. On acidic homogeneous and heterogeneous catalysts, such as. B. tungsten trioxide on titanium dioxide can on this Way with isobutene conversions up to 95%, a discharge stream can be obtained has a residual isobutene content of up to 5%.

Feed cleaning of the raffinate II stream on adsorber materials

To improve the service life of the catalysts used for the subsequent metathesis step is, as described above, the use of a Feed cleaning (guard bed) for separating catalyst poisons, such as for example water, oxygenates, sulfur or sulfur compounds or organic halides required.

Examples of processes for adsorption and adsorptive cleaning are described in W. Kast, adsorption from the gas phase, VCH, Weinheim (1988). The use of zeolitic adsorbents is explained at D.W. Breck, Zeolite Molecular Sieves, Wiley, New York (1974).

The removal of especially acetaldehyde from C ₃ to C ₁₅ hydrocarbons in the liquid phase can be carried out in accordance with EP-A-0 582 901.

Selective hydrogenation of crude C ₄ cuts

From the raw C ₄ fraction originating from a steam cracker or a refinery, butadiene (1,2- and 1,3-butadiene) and alkynes or alkenins contained in the C _{4 cut} are selectively hydrogenated in a two-stage process. According to one embodiment, the C ₄ stream originating from the refinery can also be fed directly into the second step of the selective hydrogenation.

The first step of the hydrogenation is preferably carried out on a catalyst which contains 0.1 to 0.5% by weight of palladium on aluminum oxide as a support. The reaction is carried out in the gas / liquid phase in a fixed bed (trickle mode) with a liquid circuit. The hydrogenation takes place at a temperature in the range from 40 to 80 ° C. and a pressure of 10 to 30 bar, a molar ratio of hydrogen to butadiene from 10 to 50 and a volume velocity LHSV of up to 15 m ³ fresh feed per m ³ catalyst per hour and one Ratio of recycle of inflow operated from 5 to 20.

The second step of the hydrogenation is preferably carried out on a catalyst which contains 0.1 to 0.5% by weight of palladium on aluminum oxide as a support. The reaction is carried out in the gas / liquid phase in a fixed bed (trickle mode) with a liquid circuit. The hydrogenation takes place at a temperature in the range from 50 to 90 ° C. and a pressure from 10 to 30 bar, a molar ratio of hydrogen to butadiene from 1.0 to 10 and a volume velocity LHSV from 5 to 20 m ³ fresh feed per m ³ catalyst operated per hour and a recycle to inflow ratio of 0 to 15.

The hydrogenation is carried out under so-called "low isom" conditions, under which result in no or at least minimal C = C isomerization of 1- Butene comes to 2-butene. The residual butadiene content can vary depending on Hydrogen sharpness be 0 to 50 ppm.  

The reaction product obtained in this way is referred to as raffinate I and also has Isobutene 1-butene and 2-butene in a molar ratio of 2: 1 to 1:10, preferably from 2: 1 to 1: 2.

Alternatively: separation of butadiene from crude C _{4 cut} via extraction

Butadiene is extracted from crude C ₄ cuts using BASF technology using N-methylpyrrolidone.

The reaction discharge of the extraction is carried out according to an embodiment of Invention in the second step of the previously described Selective hydrogenation fed to remove residual butadiene, wherein care should be taken to ensure that there is no or only slight isomerization of 1-butene comes to 2-butene.

Separation of isobutene via etherification with alcohols

In the etherification stage, isobutene is mixed with alcohols, preferably with Isobutanol, on an acid catalyst, preferably on an acid catalyst Ion exchanger, converted to ether, preferably isobutyl tert-butyl ether. The According to one embodiment of the invention, implementation takes place in one three-stage reactor cascade, in the flooded fixed bed catalysts from top to bottom flowed through below. The inlet temperature in the first reactor is 0 up to 60 ° C, preferably 10 to 50 ° C; the initial temperature is between 25 and 85 ° C, preferably between 35 and 75 ° C, and the pressure is 2 to 50 bar, preferably 3 to 20 bar. With a ratio of isobutanol to isobutene from 0.8 to 2.0, preferably 1.0 to 1.5, the conversion is between 70 and 90%.

In the second reactor, the inlet temperature is 0 to 60 ° C, preferably 10 up to 50 ° C; the initial temperature is between 25 and 85, preferably  between 35 and 75 ° C, and the pressure is 2 to 50 bar, preferably 3 to 20 bar. The total turnover over the two stages increases to 85 to 99%, preferably 90 to 97%.

In the third and largest reactor at the same inlet and outlet temperature from 0 to 60 ° C, preferably 10 to 50 ° C; the equilibrium turnover achieved. The ether cleavage follows the etherification and separation of the ether formed: the endothermic reaction is carried out on acidic catalysts, preferably on acidic heterogeneous contacts, for example phosphoric acid on an SiO _{2 support} , at an inlet temperature of 150 to 300 ° C., preferably at 200 to 250 ° C, and an initial temperature of 100 to 250 ° C, preferably at 130 to 220 ° C.

When using FCC-C ₄ cuts, it is to be expected that propane in amounts of 1% by weight, isobutene in amounts of 30 to 40% by weight and C ₅ hydrocarbons in amounts of 3 to 10% will be introduced , which can impair the subsequent process sequence. Accordingly, the possibility of a distillative separation of the components mentioned is provided as part of the processing of the ether.

The reaction product thus obtained, referred to as raffinate II, has one Residual isobutene content of 0.1 to 3 wt .-%.

In the case of larger amounts of isobutene in the discharge, for example when using FCC-C ₄ fractions or when separating isobutene by means of acid-catalyzed polymerization to give polyisobutene (partial conversion), the remaining raffinate stream can be prepared by distillation according to one embodiment of the invention before further processing.

Purification of the raffinate II stream on adsorber materials

The raffinate II stream obtained after the etherification / polymerization (or distillation) is purified on at least one guard bed consisting of high-surface area aluminum oxides, silica gels, aluminum silicates or molecular sieves. The protective bed serves to dry the C ₄ stream and to remove substances which can act as a catalyst poison in the subsequent metathesis step. The preferred adsorbent materials are Selexsorb CD and CDO as well as 3Å and NaX molecular sieves (13X). Cleaning takes place in drying towers at temperatures and pressures that are selected so that all components are in the liquid phase. If necessary, the cleaning step for feed preheating is used for the subsequent metathesis step.

The remaining raffinate II stream is almost free of water, oxygenates, organic chlorides and sulfur compounds.

When performing the etherification step with methanol to produce MTBE can do it due to the formation of dimethyl ether as a minor component it may be necessary to combine several cleaning steps or one after the other to switch.

In order to maximize the yield of 2-pentene and 3-hexene, the following variants, which are explained below in the drawing in FIG. 1, FIG. 2 and FIG. 3 using simplified process diagrams, are preferred in the process according to the invention. For a better overview, the reactions are shown without significant amounts of isobutene in the C ₄ feed. Here mean:

C ₂ = ethene
C ₃ = propene
C ₄ = 1- and 2-butene
C ₄ ¯ = n- and i-butane
C ₅ ¯ = 2-pentene
C ₆ = 3-hexene
C ₄ -Re = C ₄ -Recycle
n-Bu = n-butenes
C _4/5 -Re = C _4/5 -Recycle
C ₅ -Re = C ₅ -Recycle

Metathesis with two-stage distillation and partial C ₄ recycling Obtaining 2-pentene and 3-hexene ( Fig. 1)

The discharge stream of the metathesis reactor R consisting of C ₂ -C ₆ olefins and butanes is separated in the distillation D1 into a fraction of ethene, propene and 0 to 50% of the unreacted butenes and butanes, which are optionally fed into the processing sequence of a cracker , as well as a high boiler fraction consisting of residual C ₄ and 2-pentene and 3-hexene formed. The latter is distilled in a column D2 to obtain 2-pentene as a side draw and 3-hexene. Both flows occur with a purity of <99%. The C ₄ fraction is withdrawn overhead and returned to the metathesis reactor R. Column D2 can also be designed as a dividing plate column. The reactor R and the column D1 can be coupled to form a reactive distillation unit.

The top discharge from the distillation column D1 can be recycled to the metathesis reactor R to increase the yield of C ₅ / C ₆ olefins if necessary.

Metathesis step with two-stage distillation and partial C ₄ and C ₅ recycling Maximizing Witch Yield ( Fig. 2)

The discharge stream of the metathesis reactor R consisting of C ₂ -C ₆ olefins and butanes is separated in the distillation D1 into a fraction of ethene, propene and 0 to 50% of the unreacted butenes and butanes, which are optionally fed into the processing sequence of a cracker , as well as a high boiler fraction consisting of residual C ₄ and 2-pentene and 3-hexene formed. The latter is distilled in a column D2 to obtain 3-hexene, which is isolated with a purity of <99%. The C ₄ fraction is taken together with pentene overhead and returned to the metathesis reactor R. The reactor R and the columns D1 and D2 can be coupled to form a reactive distillation unit.

Metathesis step with three-stage distillation / partial C ₄ and C ₅ recycling to maximize the hexene yield ( FIG. 3)

The discharge stream of the metathesis reactor R consisting of C ₂ -C ₆ -olefins and butanes is separated in the distillation D1 into a low boiler fraction consisting of ethene and propene, which can either be fed into the processing sequence of a cracker or, preferably, into a further distillation column D3 into the Pure components ethene and propene is separated, and in a high boiler fraction consisting of C ₄ -olefins and butanes as well as formed 2-pentene and 3-hexene. The latter is separated in a column D2, which can optionally be designed as a side draw column or dividing wall column, into a low-boiling fraction consisting of C ₄ -olefins and butanes, which can be entirely or partially recycled to the metathesis step, into a preferably consisting of 2-pentene Medium boiler fraction, which can be entirely or partially returned to the metathesis step, and into a 3-hexene (purity of <99%) valuable product high boiler fraction, which is discharged.

Catalysts known from the literature are heterogeneous rhenium catalysts, such as Re ₂ O ₇ on γ-Al ₂ O ₃ or on mixed supports, such as, for. B. SiO ₂ / Al ₂ O ₃ , B ₂ O ₃ / SiO ₂ / Al ₂ O ₃ or Fe ₂ O ₃ / Al ₂ O ₃ with different metal content is preferred. The rhenium oxide content is between 1 and 20%, preferably between 3 and 10%, regardless of the carrier selected.

The catalysts are used freshly calcined and do not require any further activation (e.g. by alkylating agent). Deactivated catalyst can by burning off coke residues at temperatures above 400 ° C in the air flow and cooling several times under an inert gas atmosphere be regenerated.

Homogeneous catalysts are less suitable, but can nevertheless be used according to the invention, some of which are more active, but have a comparatively significantly shorter service life:
KJ Ivin, J. Organomet. Catal. A: Chemical 1998, 133, 1-16; KJ Ivin, LC. Mol, Olefin Metathesis and Metathesis Polymerization, 2 ^nd edition, Academic Press, New York, 1996; GW Parshall, SD Ittel, Homogeneous, Catalysis, 2nd ed., 1992, John Wiley & Sons, New York, Chichester, Brisbane, Toronto, Singapore, pp. 217ff; RH Grubbs in Prog. Inorg. Chem., S. Lippard (ed.), John Wiley & Sons, New York, 1978, Vol. 24, 1-50; RH Grubbs in Comprehensive Organomet. Chem., G. Wilkinson (ed.), Pergamon Press, Ltd., New York, 1982, Vol. 8, 499-551; DS Breslow, Prog. Polym. Sci. 1993, Vol. 18, 1141-1195] as well as protic medium and homogeneous metathesis catalysts stable to atmospheric oxygen, such as that of RH Grubbs et al. defined ruthenium alkylidene compounds of the general composition RuX ₂ (= CHR) (PR ' ₃ ) ₂ (R = R') described in WO 93/20111, WO 96/04289, WO 96/06185, WO 97/03096 and WO 98/21214 = Alkyl, aryl) and "in situ" from [Ru (n ⁶ -aryl) X ₂ ] ₂ , phosphines PR ₃ and diazo compounds RCHN ₂ mixtures produced, on their suitability as a metathesis catalyst AF Noels in J. Chem. Soc., Chem Commun. 1995, 1127-1128.

In contrast, heterogeneous catalysts, in particular molybdenum, tungsten and rhenium oxides on inorganic oxide supports, which are optionally pretreated with alkylating agents, often prove to be more sensitive to impurities in the feed. Their advantage over homogeneous catalysts with higher activity lies in the very simple catalyst regeneration, which usually takes place by burning off coke residues in the air stream. A comparison of the heterogeneous contacts shows that Re ₂ O ₇ / Al ₂ O _{3 is} already active under very mild reaction conditions (T = 20 to 80 ° C), while MO ₃ / SiO ₂ (M = Mo, W) only at temperatures developed above 100 to 150 ° C activity and can therefore occur as side reactions C = C double bond isomerization.

The following should also be mentioned:

• - WO ₃ / SiO ₂ , prepared from (C ₅ H ₅ ) W (CO) ₃ Cl and SiO ₂ in J. Mol Catal. 1995, 95, 75-83;
• - 3-component system, consisting of [Mo (NO) ₂ (OR) ₂ ] _n , SnEt ₄ and AlCl ₃ in J. Mol. Catal. 1991, 64, 171-178 and J. Mol. Catal 1989, 57, 207-220;
• - Nitridomolybdenum (VI) complexes from highly active precatalysts in J. Organomet. Chem. 1982, 229, C ₁₉ -C ₂₃ ;
• - heterogeneous SiO ₂ -based MoO ₃ and WO ₃ catalysts in J. Chem. Soc., Faraday Trans. / 1982, 78, 2583-2592;
• - supported Mo catalysts in J. Chem. Soc., Faraday Trans./1981, 77, 1763-1777;
• - Active tungsten catalyst precursor in J. Am. Chem. Soc. 1980, 102 (21), 6572-6574;
• Acetonitrile (pentacarbonyl) tungsten in J. Catal. 1975, 38, 482-484;  
• - Trichloro (nitrosyl) molybdenum (II) as a catalyst precursor in Z. Chem. 1974, 14, 284-285;
• - W (CO) ₅ PPH ₃ / EtAlCl ₂ in J. Catal. 1974, 34, 196-202;
• - WCh / n-BuLi in J. Catal 1973, 28, 300-303;
• - WCl ₆ / n-BuLi in J. Catal. 1972, 26, 455-458;

FR 2 726 563 O ₃ ReO [Al (OR) (L) xO] nReO ₃ with R = C ₁ -C ₄₀ hydrocarbon, n = 1-10, x = 0 or 1 and L = solvent, EP-A- 191 0 675, EP-A-129 0 474, BE 899897 catalyst systems made of tungsten, 2 substituted phenolate residues and 4 other ligands, including a halogen, alkyl or carbene group.

FR 2 499 083 catalyst system made of a tungsten, molybdenum or rhenium Oxo transition metal complex with a Lewis acid.

US 4,060,468 catalyst system from a tungsten salt, an oxygen-containing aromatic compound, e.g. B. 2,6-dichlorophenol and optionally molecular Oxygen.

BE 776,564 catalyst system from a transition metal salt, one organometallic compound and an amine.

To improve the cycle time of the catalysts used, especially the supported catalysts, the use of feed cleaning on adsorber beds (guard beds) is recommended. The protective bed serves to dry the C ₄ stream and to remove substances which can act as a catalyst poison in the subsequent metathesis step. The preferred adsorbent materials are Selexsorb CD and CDO as well as 3Å and NaX molecular sieves (13X). Cleaning takes place in drying towers at temperatures and pressures, which are preferably chosen so that all components are in the liquid phase. If necessary, the cleaning step for feed preheating is used for the subsequent metathesis step. It can be advantageous to combine several cleaning steps with each other or to connect them in series.

Pressure and temperature in the metathesis step are chosen so that all Reactants are present in the liquid phase (usually = 0 to 150 ° C, preferably 20 to 80 ° C; p = 2 to 200 bar). Alternatively, it can be beneficial be, especially for feed streams with a higher isobutene content, the implementation perform in the gas phase and / or use a catalyst that has a lower acidity.

As a rule, the reaction is after 1 s to 1 h, preferably after 30 s to 30 min ended. You can continuously or batchwise in reactors such as Pressurized gas vessels, flow tubes or reactive distillation devices be carried out, flow tubes are preferred.

Examples example 1 Continuous experiment for the two-stage selective hydrogenation of crude C ₄ cut

Crude C _{4 cut} with a composition of 43.7% butadiene (incl. Butenin and butyne), 14.3% 1-butene, 7.8% 2-butenes and 7.2% n-butane is continuous in one flowed through tube reactor at 0.3% Pd / Al ₂ O ₃ heterogeneous contact with a fish inlet of 1 kg / h raw C _{4 cut} and a circuit of 8.2 kg / h with an LHSV of 9.0 h ^-1 at a reactor inlet temperature of 20 ° C with 175 Nl / h of hydrogen. With a butadiene conversion of 95.2%, a total butene selectivity of 99.6% and a 1-butene selectivity of 56.5% were achieved in the first stage of the selective hydrogenation under these conditions.

A typical reaction discharge from the first stage of the selective hydrogenation, consisting of 0.61% butadiene (incl. Butenin and butyne), 26.9% 1-butene, 14.9% 2-butenes and 11.6% n-butane, is given in a continuously flowed tube reactor at 0.3% Pd / Al ₂ O ₃ heterogeneous contact (H0-13L) with a fish inlet of 2.2 kg reaction output of the 1st stage and a circuit of 4.0 kg / h with an LHSV of 20 h ^-1 at a reactor inlet temperature of 60 ° C and a reactor outlet temperature of 70 ° C with 16 Nl / h of hydrogen. With a butadiene conversion of 99.2%, a raffinate I stream was obtained under these conditions with a 1-butene content of 58.2%, which had a residual content of 48 ppm butadiene.

Example 2 Continuous attempt to separate isobutene by etherification with isobutanol

In a three-stage reactor cascade, a flooded and acidic Fixed bed equipped with ion exchanger from top to bottom with raffinate I and Flows through isobutanol, the ratio of isobutanol to isobutene in the feed was set to 1.2. The reactor inlet temperature is 40 ° C, the Reactor outlet temperature at 65 ° C and the reaction pressure at 8 bar. The measured isobutene conversion after the first stage is 85%. In the second, similarly sized reactor sales at a Reactor inlet temperature of 40 ° C, a reactor outlet temperature at 50 ° C and a reaction pressure of 8 bar increased to 95%. In the third, clearly equilibrium conversion at a larger reactor Reactor inlet temperature and reactor outlet temperature of 40 ° C each and a reaction pressure of 8 bar. The one under these conditions raffinate remaining after separation of isobutyl tert-butyl ether by distillation Electricity has a residual isobutene content of 0.7%.  

Example 3 Continuous attempt at the one-step metathesis of raffinate II

After cleaning the feed via an adsorber bed made of 13X molecular sieve, a mass flow of 1300 g with a dwell time of 3 min is used to make 43.5% 1-butene, 36.2 2-butene, 2.0% isobutene and 18.3% butanes C ₄ fraction at 40 ° C and 10 bar (liquid phase) continuously passed through a flow tube equipped with Re ₂ O ₇ / Al ₂ O ₃ heterogeneous contact. The reaction product is separated in a two-stage distillation sequence, with a C ₂ / C ₃ / C ₄ low-boiling phase consisting of 1.2% ethene, 38.7% propene, 31.3% butenes, 2 in the first column at 10 bar , 9% isobutene and 25.9% butanes is taken overhead. The bottom consisting of 28.0% butenes, 1.3% isobutene, 20.4% butanes, 27.8% 2-pentene and 21.9% 3-hexene is then fed to a second column operated at 2 bar, in which the CVC ₅ low boiler fraction is removed overhead and completely returned to the metathesis reaction. The high boiler fraction obtained in the swamp consisted of 99.5% 3-hexene. The percentages correspond to the corresponding proportions by mass. The determined butene sales are 91% for 1-butene and 50% for 2-butene. The determined space-time yields were on average 700 g / lh propene or 760 g / lh 3-hexene.

Claims (11)

1. A process for the preparation of C ₅ - / C ₆ -olefins from an olefinic C ₄ - hydrocarbon-containing starting stream, characterized in that

• a) in the presence of a metathesis catalyst which contains at least one compound of a metal of VI.b, VII.b or VIII. Subgroup of the Periodic Table of the Elements, a metathesis reaction is carried out, within the scope of which 1-butene, 2-butene and Isobutene are converted to a mixture of C ₂ -C ₆ olefins and butanes,
• b) the discharge stream thus obtained is first separated by distillation into a low boiler fraction A consisting of C ₂ -C ₄ olefins and butanes or of C ₂ -C ₃ olefins, which is discharged, and into a C ₄ -C ₆ olefin and butanes existing high boiler fraction,
• c) the high boiler fraction obtained from b) is then separated by distillation into a low boiler fraction B consisting of butenes and butanes, a medium boiler fraction C consisting of pentene and methylbutene and a high boiler fraction D consisting of hexene and methylpentene,
• d) wherein the fractions B and / or C are completely or partially returned to process step a) and the fraction D is discharged as a product.

2. The method according to claim 1, characterized in that a C ₄ fraction is used, as is obtained in steam or FCC cracking or in the dehydrogenation of butane. 3. The method according to claim 1 or 2, characterized in that raffinate I or II is used as the C ₄ fraction, the C ₄ stream being freed from disturbing impurities by appropriate treatment on adsorber protective beds before the metathesis reaction. 4. The method according to any one of claims 1 to 3, characterized in that the Metathesis reaction in the presence of heterogeneous metathesis catalysts is carried out from the class of inorganic carriers applied transition metal compounds of metals of VI.b, VII.b or VIII. Group of the Periodic Table of the Elements are selected. 5. The method according to claim 4, characterized in that rhenium oxide on γ-aluminum oxide or on Al ₂ O ₃ / B ₂ O ₃ / SiO ₂ mixed carriers is used as the metathesis catalyst. 6. A process for the preparation of C ₅ - / C ₆ -olefins and propene from steam cracker or refinery C ₄ streams, comprising the substeps

• 1. Separation of butadiene and acetylenic compounds by optionally extracting butadiene with a butadiene-selective solvent and subsequently / or selectively hydrogenating butadienes and acetylenic impurities contained in crude C ₄ cut in order to obtain a reaction product, the n-butenes and isobutene and contains essentially no butadienes and acetylenic compounds,
• 2. Separation of isobutene by reaction of the reaction product obtained in the above step with an alcohol in the presence of an acid catalyst to give an ether, separation of the ether and alcohol, which can be carried out simultaneously or after etherification, in order to obtain a reaction product which n -Butene and optionally oxygenate impurities, whereby formed ether can be discharged or split back to obtain pure isobutene and the etherification step can be followed by a distillation step to separate isobutene, with C ₃ -, iC ₄ - and C ₅ -hydrocarbons also possibly being introduced by distillation can be separated in the course of working up the ether,
• 3. separation of the oxygenate impurities from the discharge of the above steps on appropriately selected adsorber materials,
• 4. metathesis reaction of the raffinate II stream thus obtained according to one of claims 1 to 5.

7. The method according to claim 6, characterized in that the sub-step selective hydrogenation of butadienes contained in crude C _{4 cut} and acetylenic impurities is carried out in two stages by contacting the raw C _{4 cut} in liquid phase with a catalyst which contains at least one metal , selected from the group consisting of nickel, palladium and platinum, on a support, at a temperature of 20 to 200 ° C, a pressure of 1 to 50 bar, a volume velocity of 0.5 to 30 m ^{3 of} fresh feed per m ^{3 of} catalyst per Hour and a recycle to feed ratio of 0 to 30 with a molar ratio of hydrogen to diolefins of 0.5 to 50 to obtain a reaction product in which, in addition to isobutene, the n-butenes 1-butene and 2-butene in a molar ratio from 2: 1 to 1:10, preferably from 2: 1 to 1: 2, and essentially no diolefins and acetylenic compounds are present. 8. The method according to claim 6 or 7, characterized in that the sub-step butadiene extraction from crude C _{4 cut} with a butadiene-selective solvent selected from acetone, furfural, acetonitrile, dimethylacetamide, dimethylformamide and N-methylpyrrolidone is carried out to to obtain a reaction discharge in which the n-butenes 1-butene and 2-butene are present in a molar ratio of 2: 1 to 1:10, preferably 2: 1 to 1: 2. 9. The method according to any one of claims 1 to 8, characterized in that the Sub-step with isobutene etherification in a three-stage reactor cascade Methanol or isobutanol in the presence of an acidic ion exchanger is carried out in the flooded fixed bed catalysts from top to bottom are flowed through, the reactor inlet temperature 0 to 60 ° C, the Initial temperature 25 to 85 ° C, the pressure 2 to 50 bar and the ratio of isobutanol to isobutene is 0.8 to 2.0 and the total conversion is Equilibrium turnover corresponds. 10. The method according to any one of claims 1 to 8, characterized in that the Sub-step isobutene separation by oligomerization or polymerization of isobutene starting from that following the steps described above Butadiene extraction and / or selective hydrogenation obtained reaction discharge in the presence of a catalyst which is selected from heterogeneous contacts, which are an oxide of a metal of subgroup VI.b. Periodic table of the elements on an acidic inorganic carrier included to produce a current that is less than 1% Has residual isobutene content.   11. The method according to claim 1, characterized in that the substep Feed cleaning on at least one Guard Bed consisting of high surface area aluminum oxides, silica gels, alumosilicates or Mol sieves is carried out.